1. Field of the Invention
The present invention relates to a stepping motor unit having a stepping motor which is mounted to an annular motor mount, for example in an automatic focus and exposure camera.
2. Description of the Related Art
In an automatic focus and exposure camera in which the focus adjustment and the exposure control are successively effected in accordance with the shutter release operation, a focusing lens is moved to a focused position by a stepping motor in association with the shutter releasing operation. Then, a lens shutter is driven by the stepping motor. The stepping motor usually has a rotor consisting of a cylindrical double-pole permanent magnet and a plurality of stators having coils, so that the rotor is located between the stators. The magnetic poles of the coils change in accordance with pulse signals input thereto to rotate the rotor through a predetermined number of steps.
Upon incorporating the stepping motor in an automatic focus and exposure camera, the stepping motor is usually mounted to an annular motor mount provided in a lens barrel. The stators are usually located on the opposite sides of the rotor in a linear arrangement in which the stators are aligned along a line or in an archform arrangement in which the stators are located along a circle.
However, in the former type of arrangement, since the stators are aligned along a line on the annular (circular) motor mount, a compact and practical arrangement of the stators not be realized.
On the other hand, in the latter type of arrangement, since the stators are formed archwise, coil holding portions on which the coils are provided are also formed in the shape of an arch, and it is very difficult to effectively wind the coils on the corresponding arch-shaped bobbins. This results in a large size but decreased number of coil turns.